script: support multi-stream logging

script: support multi-stream logging

* allow to use --log-in <infile> and --log-out <outfile> in the same time
* add --log-io <file> to log stdout and stdin to the one log file
* introduce a new timing file format with entry type identifirs

   I <delay> <size>   : info about input stream
   O <delay> <size>   : info about output stream

in the next commits it's possible to add 'S' for signals and 'H' for
extra (header) information.

* the new file format is optional and enabled only if multiple streams
  logging is requested.

Signed-off-by: Karel Zak <kzak@redhat.com>